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ISL55210IRTZ-T7A Datasheet(PDF) 10 Page - Intersil Corporation |
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ISL55210IRTZ-T7A Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 18 page ISL55210 10 FN7811.0 March 2, 2011 Applications Basic Operation The ISL55210 is a very wideband, voltage feedback based, differential amplifier including an output common mode control loop and optional power shutdown feature. Intended for very low distortion differential signal driving, this non-unity gain stable device also delivers extremely low input noise terms of 0.85nV/√Hz and 5pA/√Hz. Most applications are intended for AC coupled I/O using a single 3.3V supply. It will operate over a single supply range of 3.0V to 4.2V. Where DC coupled operation is desired, using split power supplies will allow the ISL55210 I/O common mode range limits to be observed while giving either a differential I/O or single to differential configuration. Most applications behave as a differential inverting op amp design. There is, therefore, an input gain resistor on each side of the inputs that must be driven. To retain overall low output noise, these resistors are normally of low value. The device can be powered down to <400µA supply current using the optional disable pin. To operate normally, this pin should be asserted high using a simple logic gate to +VS or tied high through a 10kΩ resistor to +VS. When disabled, the power dissipation drops to <1mW but, due to the inverting op amp type architecture, the input signal will feed forward through the external resistors giving limited isolation. Application and Characterization Circuits The circuit of Figure 28 forms a starting point for many of the characterization curves for the ISL55210. Since most lab sources and measurement devices are single-ended, this circuit converts to differential at the input through a wideband transformer and would also be a typical application circuit coming from a single ended source. Assuming the source is a 50Ω impedance, the RG resistors are set to provide both the input termination and the gain. Since the inverting summing nodes act as virtual ground points for AC signal analysis, the total termination impedance across the input transformer secondary will be 2 * RG. Setting this equal to n2*RS will give a matched input impedance inside the bandwidth of the transformer (where "n" is the turns ratio). The amplifier gain is then set by adjusting the feedback resistors values. Since the ISL55210 is a VFA design, increasing the feedback resistor to get higher gain does not directly reduce the bandwidth as it would with a CFA based design. This gives increased flexibility in the input turns ratio and overall gain setting (while holding a matched input impedance) over alternate solutions. Working with a transformer coupled input as shown in Figure 28, or with two DC blocking caps from a differential source, means the output common mode voltage set by either the default internal VCM setting, or a voltage applied to the VCM control pin, will also appear as the input common mode voltage. This provides a very easy way to control the ISL55210 I/O common mode operating voltages for an AC coupled signal path. The internal common mode loop holds the output pins to VCM and, since there is no DC path for an ICM current back towards the input in Figure 28, that VCM setting will also appear as the input common mode voltage. It is useful, for this reason, to leave any input transformer secondary centertap unconnected. The internally set VCM voltage is referenced from the negative supply pin. With a single 3.3V supply, it is very close to 1.2V but will change with total supply voltage across the device as shown in Figure 26. FIGURE 26. DEFAULT VCM AND MAX VOPP vs SUPPLY VOLTAGE FIGURE 27. SUPPLY CURRENT vs SUPPLY VOLTAGE Typical Performance Curves V S+ = 3.3V, TA ≈ +25°C, unless otherwise noted. (Continued) 1 2 3 4 5 6 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 4.3 4.4 4.5 SUPPLY VOLTAGE (V) TEST CIRCUIT #1 INTERNALLY SET VCM MAXIMUM DIFFERENTIAL VP-P OUTPUT USING DEFAULT VCM 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 4.3 4.4 4.5 SINGLE SUPPLY VOLTAGE (V) TEST CIRCUIT #1 TA = +25°C TA = -40°C TA = +85°C 50 1:1.4 1µF 1µF 85 ISL55210 +3.3V + - VI 50 50 35 35 ADT2-1T 0.1uF 200 VCM 200 200 33mA 110mW 1:1 ADT1-1WT 50 1µF VM VO RG RG RF RF 10k PD 200 LOAD 85 1µF FIGURE 28. TEST CIRCUIT #1 |
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